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Video Cables [MEGA LONG] All you need to know?

Discussion in 'Cables & Switches' started by Nic Rhodes, Dec 10, 2003.

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  1. Nic Rhodes

    Nic Rhodes
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    Video Cables [MEGA LONG] All you need to know?

    Inspired several things, I decided to write the following article:

    The general lack of understanding of what it is needed for a cable, I have tried to capture what is required on cables / wire in each area and recommend the best ‘raw’ off the reel cables I know of. I am not endorsing any commercial finished product like Chord, IXOS, QED but trying to educate people how to make the near perfect cable for a specific application that will satisfy most if not all. I will steer you towards commercial off the reel cables I feel are without peer and could be the basis of your cable needs. You will need to buy these / find someone who uses them to take advantage of this performance You can then go away and buy cables, informed with what I at least think important (and professional broadcaster, cable manufacturers etc etc). I would welcome any serious input from others to widen the debate further. This is NOT to say that other manufacturers don’t also make great products, I am sure they do, but I have sourced cables from the large cable manufacturers (who supply most people anyway) rather than the ‘audio / video brands’ mentioned above.

    Please don’t flame me just because you use xxxx brand (substitute you favourite here) and it works in your system. Please have a pop if your cable outperforms the basic stuff I am recommending here and you have both to try at home and let us know why it is better than my suggestion. I will be the first to try it out in my never ending quest for the ultimate. I have said repeatedly here, I also want to learn and welcome all inputs, expert to amateur. I am NOT telling you what to buy but I am hopefully advising / steering / helping you with what is important (technically), and what works (or what I think is important). This is VERY different to telling people to buy IXOS etc. The stuff I am suggesting you look at is I believe of the HIGHEST quality (and I mean TOP) but it will surprize many just how little it cost to do correctly, certainly less than most of you currently spend. It is, I think, an upgrade to what most people currently use. If you don’t agree please say so WITH the reasons why you disagree having tried what I am endorsing. I can easily live with that as an informed opinion but what I don’t want to hear is brand X works great for me. It helps no one.

    There is way to much ‘part’ information out there and hopefully this will give you ALL you need to buy a cable for you application. There is way too much RG X is all you need, when what you need to know is why RG X version A is SOO much better than version B. [The devil is in the detail] I am as guilty as anyone on this so hopefully this corrects this. I get so fed up when I see people say for the ‘demanding’ application, say video leads all you need is RG 6 cable with a 3 GHz bandwidth. This is a classic example of either ‘some luck’ or only partial understanding of the problem involved with cables for this application. Sure the ultimate cable ‘may’ have an RG 6 designation with 3Ghz capability but these are NOT what we should be interested in (even the best crimp RCA plugs only have a 200 MHZ bandwidth!!!!!). We should be much more concerned with low capacitance, a linear 75 Ohm CI (Characteristic Impedance) along the WHOLE cable and excellent screening capabilities. The hard truth is MOST RG 6 do NOT met these specifications, particularly in the CI profile down a cable. The cables I will point you to DO meet these exacting criteria. The cables are designed for no compromises but luckily are affordable and once again I will say there are always other solutions out there from commercial companies. All I would ask is “are you SURE your current cable can compete?”

    But what really bugged me was when an ‘audiophile’ cable company (actually just a plug soldering company when I knew then best) complained we weren’t taking cables seriously when we had a recent ‘Event’. The truth couldn’t have been further from the truth, we were using some of the best cables we knew about but they weren’t from the said company X. Mind you they were particularly slow in coming forward to help, I wonder why?

    I work for NO cable company or AV company so I make NO money from any of this. [This always comes up!] I leave it to others. I am just explaining what you need to know in order to get a great performing cable at a great price.

    I will try and cover:

    The basic of cables (in general), electric and physical

    Analogue video cables
    Digital video cables

    I have included balanced cables so people understand how these work (wrt noise)

    This by definition might also cover what you need to know for most of the ‘other’ leads. You make you own extrapolations here though ;) It may surprize many just how high performance video cables also make great ‘other’ leads (but not the other way round). I will talk about sub woofer cables though as I think this is an under discussed topic and needs special attention.


    So the emphasis is on digital (SDI) video and analogue video.

    Mains issues and mains cables as they are closely related will be dealt with later and I will spin this off into it’s own thread if there is interest but this will take time.

    Cables can make a difference, in fact they can make a great difference but if there is a difference in two cables then chances are one is probably not doing something correctly in the first place. Top performing cable is NOT expensive and the cables I am recommending are all basically only a £1- 4/ m (or similar) to which they need to be terminated etc. (I will cover that as well). I believe they will outperform or equal ANYTHING I have ever tested here. Just for the record I have many examples here I have had on test and these include many of the usual ‘suspects’ including silver, optical and carbon cables in addition to the ‘copper’ based stuff I will talk about here. If anyone met me at The Event 11, the scaler room (and bits elsewhere) were cabled with some of my collection. I basically came to the Event 11 with 1/3 of my stock of cables and it filled the boot of a family saloon!! These are not wide, unsubstantiated results, it is what I believe works best in each situation. In fact if you look at ‘more innovative’ cable suppliers on the forums, you may notice some simularities. I make no claims for originality, many other have discovered this before me and after me. They do work though and work very well. I thought it a good time to pull it all together.

    This was an oddessy that start out with me learning how to make balanced digital cables for small money, it has evolved into an obsession.

    Remember Do everything in Excess even Excess :)
    Pre amble over so:
     
  2. Nic Rhodes

    Nic Rhodes
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    The basics
    The extent to which a cable deviates from an ‘ideal’ is directly related to the physical structure of the cable and its connectors. Cables does three important things to a signal:

    1 attenuates the signal
    2 contributes its own inductive and capacitive ‘reactance’
    3 exposes the signal to electromagnetic energy from other sources

    The extent to which a cable does any or all of these things to a signal is determined by the cable's physical structure and the environment in which it operates.

    1 Attenuation
    Directly related cable style (coax etc) and configuration of the electrical conductors.

    2 Inductive and capacitive reactance
    Results from the physical structure of the conductors themselves, their physical placement in relation to one another, and the nature of the material placed between them (insulators / dielectric).

    3 EMF (electromagnetic fields)
    Influenced by the extent and type of shielding provided by the outer braiding of the cable.

    The above is also the same for the connectors and the electrical connection between the connector and cable, both of which are traditionally done ‘badly’. Even those of use with temperature controlled soldering stations (several :blush: ;) can’t compete with a crimp gun.

    Electricity is the flow of electrons through substances. The conductors (say copper wire) are noted for being very good for the flow of electrons. The insulators are almost impervious to electric current. The signals we are concerned with here are alternating signals (AC music signals). The electrical characteristics of a cable which most affect a delicate audio / video signal are resistance, capacitance and inductance.

    In general, a well-insulated, well-shielded, physically durable, low-capacitance cable terminated with fully-shielded, impedance-matched connectors that make sound electrical contact with both the coax and it will do exactly what it needs to do.

    Remember electrons don't know how much you spend on cable, what colour it is, whether the Germans made your plugs or the Australians, they only know what your cable looks like inside. R, C, L and CI (and screening).

    Resistance:
    A current flows through any material, no matter how conductive, some of the electrical energy is transformed into heat. This is resistance. There is no such thing as the perfect conductor (zero resistance) for audio leads, all leads have some resistance. From an audio/video perspective, it isn’t really important, it just reduces the signal strength of the signal down the wire but does NOT distort the signal per se. It just makes it a tiny bit quieter (and I mean tiny). To be honest unless you have a really high resistance, then this isn’t ‘that’ important but it is often the most quoted figure :) on spec sheets.

    Capacitance:
    Remember we are dealing with alternating current, electrons will flow into one side of the conductor, acting like they had someplace to go despite the fact that the conductors a dead end. When the voltage reverses, electrons will flow out of the conductor and into the other conductor. This repeats itself fifty times per second (say for mains). A meter hooked up to the circuit will show that a current is flowing, despite the fact that, to look at it, you'd figure there was nothing for the electricity to do. This is basically capacitance, and it is a bugger to explain properly! Low C is desirable.

    Inductance:
    When electricity flows through a wire, it creates a magnetic field around the wire, and in the case of an alternating current, that magnetic field is constantly in flux, energizing and collapsing at high speed. This magnetic field, in turn, interacts with other magnetic and electrical fields, sometimes significantly, and presents opposition to the very electrical flow, which creates it.

    The electricity doesn't flow nicely, straight from the source to the destination. It is interrupted, and altered, by the inductive properties of the wire, and some of its flow is absorbed by the capacitive properties of the wire. This is what makes cable different.

    The capacitance and inductance react differently to electrical currents at different frequencies, and that these differences have a very real ability to affect what we see and hear on our cables.

    So what do these electrical parameter do?

    Capacitance.
    This progressive roll of the upper frequencies, which are dependent on the capacitance of the cable. We therefore need to minimise capacitance as much as possible. The type of di-electric (insulator) effects the capacitance of cables but it is more complicated than that. I will explain more in the material of construction later in the article.

    Inductance
    Inductance does somewhat the same thing to the audio signal, but through different means (‘simple’ explanation). The magnetic field set up by inductance resists changes in the current flow and an AV signal is constantly changing (AC). Further, inductance doesn't resist all current flow changes equally at all frequencies. The higher the frequency, the more the inductor impedes the flow. So, what can we do to limit inductance? The main factor here is conductor length.

    Fortunately, inductance isn't a big factor at audio frequencies with normal conductor lengths; however, as we increase frequency it becomes more and more significant. Video signals, whether composite, component, or S-Video, all run at much higher frequencies. Apart from conductor length, the other considerations in limiting inductance are the cable type and plugs

    Now what else is important?

    Characteristic Impedance (CI) or Impedance matching
    An impedance matched cable is one where the impedance (that is, the sum of the capacitive and inductive reactance with the signal) of the cable is compatible with the impedances of the source of the signal and the load the signal will drive.

    Impedance matching ensures that the signal is delivered efficiently to the load. This prevents reflections (jitter / noise) and keeps the signal free of distortions. CI is irrelevant for audio frequencies BUT is important for analogue video and digital video transmission signals. I repeat it is IRRELEVANT for analogue audio signals.

    A good cable therefore has low resistance, to prevent signal loss; it has low capacitance and inductance, to prevent high-frequency loss and it's impedance matched when necessary, to do the best job of delivering the signal to its destination.

    The cable also needs to isolate the signal wire from outside influences like EMF / RFI. Insulation is the first line of electrical defence. Most cables are covered with a good insulator that keeps it from losing signal to other wires / conducting objects it meets. ('Most' as there are some nutters using a great insulator, air, by hanging wires from silk threads with no insulator!!)
     
  3. Nic Rhodes

    Nic Rhodes
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    EMF / RFI
    The electromagnetic waves in the air induce tiny current in your antenna, and your radio does the rest. But electrons, even heavy coloured ones don’t know whether the piece of wire is actually an aerial for a tuner or a wire conducting signal.

    If the problem was only radio signals, then only those of us who happen to live very close to radio transmitters would have to worry about outside electromagnetic waves getting into our audio/video gear. The reality is many sources give off electromagnetic energy. Switches, fridges, fluorescent lights, basically every electrical devise in the house!

    We therefore need proper shielding to keep this stuff out of all cables.

    A coaxial cable, instead of running its two conductors side by side like a power cord, has an outside conductor and an inside conductor, and the outside conductor is called the shield because it shields the inner conductor from the influence of outside electromagnetic energy. The shield is generally made with a woven mesh braid and / or a foil wrap.

    Radio energy and noise encounter the shield, discharge their energy to ground through the braid, and never reach the inside conductor which is carrying the delicate AV signal. If this works, then this is the end of job as the noise is never heard from again. Real life is a bit different to this however and shields (including the connector) vary quite considerable. Co ax cables have some significant advantage here for unbalanced cables.

    If a cable deals well with capacitance, inductance, attenuation, impedance matching, and shielding, it'll do right by your ears and eyes. This and the plugs / joints are all you need to get right. Each use will probably need a different balance of these characteristics but this is all you really need to do.

    The trade off’s and other stuff including the techy links
    Cables with lower capacitance can be made by moving the conductors away from each other but that would eliminate the possibility of shielding. Thick coaxial cable could be used, but we would suffer a terrible loss of flexibility and we couldn’t fit our current AV plugs on the cables! More conductive materials at the cost of conductor strength and durability; and so on, and so on. The end of the day, each cable is suitable for a variety of jobs and it is a compromise on what you use it for but it is surprizing just how many are suitable for ‘other’ uses 


    http://bwcecom.belden.com/college/college.htm

    TECHY alert, go to cable training and technical paper to find first paper on 75 ohm stuff

    RE measuring 75 Ohm CI This is REALLY difficult to do and the only company in the audio field I know have done this is Tag!

    Transmission Line Impedance
    When we talk about 75 Ohm CI we do not mean it has a linear resistance of 75 Ohm. I mean if we attach anything other than 75 Ohm CI what we mean is that if we attach a load of the specified impedance to the other end of the cable, it will look like a load of that impedance regardless of the length of the cable between.

    The reason d’etre of a 75 ohm cable is simply to match that 75 ohm impedance from point A to point B, so that as far as the devices are concerned, they're right next to one another and there are no mismatches (jitter).

    The mismatches vary in their intensity due to a variety of reasons which I won’t bother with here

    http://bwcecom.belden.com/college/college.htm

    go to cable training and technical paper to find on precision video stuff for real techies! (3 good papers)

    Transmission line impedance is critical in some applications, and not so critical in others.

    Analogue audio, particularly, CI is irrelevant because the relatively low frequencies. At normal cable lengths and even the highest SACD type frequencies the wavelength is huge (50 Khz = 6 Km). Shielding and capacitance become the dominant characteristics. If anyone talks to you about transmission lines at audio frequencies, walk away, it is simply absurd concept. This is still common in audio shops.

    But the behaviour of cables changes as signal frequencies increase and the wave length decreases. For video signals it starts becoming a serious issue. The cable length approach the wavelength of the ‘video’ signals and we start to resonate and get mismatches. 75 Ohm cable, connector and joints become VERY important now. You only have to look at the cheapest of the cheap Freeview / Sky boxes to see they all use 75 ohm CI connectors and cables. For good reason.

    This effect is dependent upon frequency, and that dependency makes it particularly relevant for digital signals. Digital signal basically switch between two states, 0 and 1s in a ‘square’ wave fashion. The digital wave is equivalent to a sine wave at that frequency accompanied by an infinite series of harmonics. Harmonics are, multiples of the frequency (1x, 2x, 3 x). If all of these harmonics aren't faithfully carried through the cable then the square wave has it’s corners rounded off. It physically isn’t possible to carry all the harmonics so this will inevitably involve some corner rounding. This imparts jitter and other issues re constitution of the digital signal. The best way to minimise this is by use impedance matched cables do for video this is 75 Ohm CI, for balanced digital audio this is 110 ohm. If the cable has a decent bandwidth this also helps but is much less of an issue than a CONSTANT linear CI (many connectors have a fraction of the bandwidth of the cables they are connected to). Many 75 ohm coax cables just do not fit this category despite ‘claiming’ 75 Ohm spec. There is a big difference in nominally identical spec cables here, the emphasis on the BIG. Don’t assume Maplin has all you need 

    Now composite, S Video and component are all 75 Ohm CI signals for analogue video. SDI is a 75 ohm CI for digital video.

    [For analogue video I recommend Belden 1505A and Belden 1694A]
    [For digital video I recommend Belden 1505A and Belden 1694A]

    Now composite, component and SDI can use ‘normal’ coax (see the Belden’s above). This howeverwill not fit into a standard mini Din plug (see below) so we need a different size of 75 Ohm cable. Here I would recommend

    [Belden 1808A (as used by Tag in their S Video cable, carefully hidden by the way!)]

    HD15 sockets are also not 75 Ohm CI but the video signal they normally carry is namely RGBHV. Many therefore like to use short break out cables (75 ohm CI) to link with some ‘bigger’ brother like above. These are ‘breakout’ cables and are popular and useful This miniature cable is the only one which physically fits the HD15 plug (VGA plug on computer). Here this is the rate-limiting step of the connector, the size of cable that can be used. (forgetting the poor CI of the plug used)

    [For Mini RGBHV I recommend Belden 1522A]

    This is excellent for this but the Vandamn ‘red’ 5 core cable is ‘popular’ as well but none of these cables are in the class of 1505A or 1694A.

    Beware of 50 Ohm coax, this is NOT what we want but is common in the computer industry (avoid RG 58 ‘style’ wire for video)

    Well know we have the best cable we can get our hands on but what about connectors.
     
  4. Nic Rhodes

    Nic Rhodes
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    Connectors: the right impedance
    Connectors and joints have CI as well, these should be matched to the cable and equipment. I will say a little about this but this article is really about cable. Information about connectors is solely so you don’t spoil good cable with in appropriate connectors

    s-video signals are 75 ohm CI as are composite and component signals and RF (FM / TV) aerial leads.

    Four-pin mini-DIN plugs on s-video are not 75 ohm CI. But there are actually 3 plug types you can use on s-video, the best is BNCs, which are 75 ohm CI (see below for more), the mini Din is just the common standard. This is why some premium kit outputs s-video on BNCs (as possible on the Tag DVD 32R) and inputs s-video on BNC (Lumagen Vision pro). They are the norm in broadcast use of this connector but domestic use has gone for mini Din, from a quality point of view I find disappointing but livable with.

    Component (inc the RGB variants) and composite are 75 Ohm CI signals. The RCA plugs used on them are not, the BNC plugs used on them are 75 ohm CI.

    RCA plugs are a decent audio connector but were never designed for video use. This is because they were designed in something like 1938 and they have a variable CI according to the design criteria!!. For audio this isn’t important, for video it is. Generally the CI of a RCA plug is about 25 Ohms. I don’t like them for these video application at all but I understand they are the norm. 75 ohm CI plugs simply don’t exist. Actually it is impossible due to the plug dimensions (a standard), but some get MUCH closer to the 75 Ohm than others. The closer the better. I have tried a variety of these ‘better’ RCAs but Canare RCAP-series crimp plugs seem to do an excellent job. As well as being the closest CI I have seen they also reap benefits from what I consider a better connection method, i.e. crimping. This is bad news but you do need a ‘special crimp’ tool :(. Canare RCAP-series crimp plugs are designed for the best possible impedance match with 75 ohm cable and equipment. All the ‘deviations’ from 75 Ohm CI progressive add up a to potentially degrade the delicate signals. Always use a cable / connector as close to the ideal as possible if given the chance.

    Eichman stuff I tried fell apart on me so I am not passing judgement yet, others have reported excellent results here. Another crimp connection I tried extensively failed physically 50% of the time. Both ‘claim’ 75 Ohm CI and are worth seriously considering. I only endorse Canare as I have found them to do the job effectively and VERY RELIABLELY. Tags says it’s plugs get close and they have ‘special’ soldering techniques which are good. This is the best ‘commercial attempt I have seen but there are other problems here….cost for that extra meter! All the rest I know are a long way from 75 Ohm CI but some look very impressive but we are talking performance not looks here.

    [As mentioned above, for audio, 75 ohm is irrelevant and therefore just a good quality plugs with a tight fit, screened etc is fine. Everyone has their favourites. I still recommend Canare RCAP-series crimp plugs here but in the solder variety Kimber, Tag are good. I use the Neutric professional one quite allot due to all the testing I do and this has a sprung ground connector. I have quite a few WBT plugs around and they look great ;)

    BNCs are a connector designed for video use (75 ohm CI). It is a cheap and HIGHLY reliable connector [There is a 50 Ohm CI variant that some people fit on some equipment, do so at you peril, it is a computer lead and the pin sizes are different]. BNCs come in crimp and solder varieties and are designed for specific cable dimensions (you match the cable to the plug type). The difference between one crimp BNC and another isn’t huge, especially in comparison with RCAs! They all work pretty well and other issues might be much more important to you like availability if coloured hoods!! (Don’t underestimate the usefulness of coloured hoods on things like RGBHV cables!!). There are quite a few good varieties of BNCs. You takes you pick really. Mine are Canare crimps again. They are reliable and probably why most of major broadcasters around the world use them. I can live with that :) as an endorsement. I am sure there are many other great varieties.

    F connectors are 75 ohm CI as used on set top box inputs as are the TV / FM aerial plugs (coax one).

    No one has a clue what the CI of a SCART plug is as it is such a poor quality connector!!

    Remember all common home video standards use 75 ohm cable. If you have balanced AES/EBU type digital audio lines, you'll want 110 ohm AES/EBU cable. Ignore any 50 ohm CI stuff (but be mindful certain aerials are 300 ohm CI, treat accordingly)

    Mini-DIN and HD-15 plugs for 75 ohm CI are a lost cause and we just have to accept there is a small loss. Many scalers actually have HD15 and BNC sockets in parallel now days. Just minimise their use where ever possible. Use BNCs over RCAs if possible for video use if you have the option. It is actually more common than you think (even my two set top boxes have composite video outputs on BNCs).

    Canare's RCAP-series plugs are a great RCA plug for video, use them where ever possible if you can on RCA sockets. Despite what people might tell you, there is NO way you can get a true 75 ohms CI plug but these babies get close. There are other RCA plugs of note, some might want to use. I prefer Canare but this is a personal choice that works for me.

    The CI of a connector with a coaxial cable, is determined by the size of the conductors, the distance between them and the type of dielectric that separates them. For RCAs this can’t ever be 75 ohm. Damage limitation is the best defence here.

    The Canare RCAP plugs have more in common with the crimp BNC plugs than they do with the ‘normal’ solder type RCA plugs. In the Canare RCAP, the coaxial cable, still encased in its dielectric, enters the rear of the connector through a perfectly round tunnel of nickel plated brass. This tunnel is sized for the specific cable diameter and hence each plug is designed for a ‘specific family’ of cables (this is their biggest drawback along with the crimp tool). The RCAP is made in numerous different sizes for each cable type and is crimped to the coax shield, it effectively replaces the stripped away shield of the coax, continuing the cable's 75 ohm impedance along toward the connector tip. At the end of the cable dielectric, the centre conductor is crimped to a gold plated pin which fits a socket centred in the plug body to make contact with the RCA plug pin. The Canare approach is thus more symetrical and effectively continues the coax cable as far into the plug as possible.

    XLR ‘balanced’ plugs also have a characteristic impedance which isn’t normally 110 Ohm. For audio it is once again not relevant but for digital once again you will find many extolling the virtues of this interface but squirt all their delicate digital 100 ohm CI signals through a non impedance matched connector just like RCAs and 75 Ohm CI. !!

    Neutrik DO make 110 ohm CI connectors for ‘digital audio’ applications and these are the plugs you need. Most people don’t use them. Why, well I simply think they don’t understand what is important. Hey, even Maplins stock them so what excuse do people have!
     
  5. Nic Rhodes

    Nic Rhodes
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    Balanced and unbalanced

    I am not going to write about the pros and cons of balanced connections. The Tag web site has done this admirably already.

    Balanced is one where two conductors, neither of which are grounded, carry the signal. A balanced line may or may not be shielded but if it is shielded, the shield is not joined to either of the two signal conductors, it is on that third pin. When one of these two conductors is carrying electrons to the source, the other is taking them away (some call this signal and return, inaccurately). The polarity of the two conductors, at any moment, is always opposite.

    Unbalanced still uses two conductors required to work. One of these conductors is attached to an external reference point ground, the other carries the signal.

    The devices are therefore balanced or un balanced and not the cable per se. The difference is in their constructions.

    Balanced cables use a symmetrical design. Examples include twisted pair telephone cable, CAT 5 computer network cable. NOTE CAT 5 / 6 cables ARE BALANCED designs. VERY IMPORTANT GUYS, remember this.;).

    Professional audio cables (analogue and digital) made for balanced operation, just like telephone cable, are usually composed of twisted pairs of insulated wire, frequently but not always shielded.

    Unbalanced cables generally take the form of coaxial cable. The two conductors in coaxial cable share a common axis (hence coax). In the centre is a signal conductor, coated with an insulating dielectric. The outside of the dielectric is a shield, consisting either of a wire braid, foil, or a combination of braid and foil, and this shield is used as the ground conductor.

    Not all cables are coax for unbalanced audio however and I will try and cover other good ways of doing something.

    http://bwcecom.belden.com/college/college.htm

    go to cable training and technical paper to find on digital studio stuff (110 Ohm)

    I have balanced and unbalanced audio kit, under normal operations there is no difference, but there is one BIG difference. Balanced and unbalanced lines use very different strategies for noise reduction, and this difference accounts for the widespread use of balanced circuits in professional audio gear, as well as for the differences in construction between balanced and unbalanced lines.

    Every cable is exposed to electromagnetic energy, which comes from other cables, from power sources, from fluorescent lights, switches, and a thousand other (mainly electrical) sources. When this energy meets a cable, the cable will absorb some of it, which causes the unwanted phenomenon we call noise.

    In unbalanced circuits you try to keep ALL NOSE OUT. They rely on the screen to block everything and pass it away to ground. The screen does not interact with the signal at all. In our perfect utopia this all works brilliantly, in reality it is a little different. Hence we have noise. See section on sub woofer cables for the extreme case.

    Balanced cables may have a shield to carry noise away to ground, just like above. But when noise does reach the inside, it strikes the two conductors. Because the conductors are closely physically associated with one another, the noise reaches them more or less simultaneously, and affects them in the same direction. The polarity of the intended signal on these two conductors is opposite in balanced operation, when one conductor is negative the other is positive, at any moment the polarity of the noise is always the same in both. This is WHY people prefer the longer leads to be balanced or the professionals prefer balanced approaches. The noise simply cancels itself out and is called common mode noise rejection.

    This is the advantage of balanced audio, it is only an advantage in noisey environments or ones that are long (and thus more susceptible to noise pick up).

    For a well screened unbalanced coax cable (see sub woofer section) there should be little difference but you already know not all coax’s are well screened don’t you.

    [For balanced work I recommend Belden 1800F (110 ohm CI)]

    Cable Design: Coax or twisted pairs

    Remember common mode noise rejection?

    It is important to use balanced cable for balanced circuits, and unbalanced cable for unbalanced circuits. Now what do I mean by this. Coax cable is designed to focus as much of the noise as possible onto the shield conductor and as little as possible onto the centre conductor. Common mode noise rejection (balanced) only works if noise affects the two conductors equally. We therefore need very different cables for these two jobs to be done effectively.

    Thus if we used coaxial cable in a balanced audio circuit, we would get plenty of noise because coax is designed to focus as much of the noise as possible onto the shield conductor and as little as possible onto the centre conductor. Common mode noise rejection only works if noise affects the two conductors equally.

    If an unshielded twisted pair was used to convey signals in an unbalanced circuit, figuring that twisted pair cables provide common mode noise rejection, we will find it doesn’t work. COMMON MODE NOISE REJECTION WON'T WORK IN AN UNBALANCED CIRCUIT, because there is ‘minimal’ current flow (noise) in the ground conductor. (There are tiny amounts there but twisted pairs are is not designed to maximise this in the screen as opposed to the coax cable!).

    Now how many twisted pairs do you see in analogue leads? The circuit accounts for common mode noise rejection and not the cable per se.

    Many ‘audiophiles’ use shielded twisted pair balanced audio cable as an unbalanced interconnects. They ground one of the two signal wires at both ends of the cable, and then ground the shield and sometimes at both ends, but sometimes only at one end, causing a loss of shield effectiveness. This increases capacitance! Something, which you will have realised by now, is the last thing we need in any cable. I found this out the hard way years ago by using un buffered passive pots as volume controls which emphasise the C problems on audio leads. Coaxial cable, not twisted pair audio cable, is the right choice when connecting unbalanced components. It has significant technical advantages.
     
  6. Nic Rhodes

    Nic Rhodes
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    Radio Guide or RG-x
    Much rubbish is talked about RG numbers. RG-6, RG-59, RG-11. This is what they are:

    RG designations stands for Radio Guide, an old military spec. Much beloved of valve data sheet collectors :blush: Coaxial cables are just one part of these specs (there is a huge class of them).

    A coax cable has two conductors, which share a single common axis. A centre conductor surrounded by a shield, the two being kept apart by a dielectric and wrapped in an outer jacket. All common video cables are coax

    Now most of this stuff was done >50 years ago and therefore now days most don’t conform to this now arbitary spec.

    All RG-6 type coaxes have an 18 AWG centre conductor. However an RG-6 might be a cheap generic low performance CATV coax, (thin aluminium braid and a copper-coated steel center conductor). It could be a better grade CATV coax, with an aluminum quad shield arrangement. If you are lucky (or smart) or it might be a precision serial digital video coax like Belden 1694A, with a dense copper braid and double-foil shield, solid copper centre conductor, nitrogen-injected PE foam dielectric, and extremely broad bandwidth and tight impedance tolerance. BIG differences in performance but all RG 6 cables.

    High bandwidth serial digital video and cable TV distribution may both use RG-6 type cable, but that doesn't mean that the cable for one is necessarily suitable for the other. There is a significant difference between these cables technically. The high bandwidth one may still be only a few pennies more however.

    RG-58 is 50 ohm CI coaxes, used in radio or in computer networks. As 50 ohm cables, these are unsuited for video / digital audio work.

    RG-6 and RG-59 are both 75 ohm CI cable types. RG-59 being the thinnest, RG-6 is slightly thicker.

    RG-6 and RG-59 are both common in home a/v use, because their sizes are compatible with a variety of connectors. Both are available in many different types, with different shields, jackets, dielectrics, and centre conductor materials.

    The best overall performance, I know, are the modern precision video (digital audio) cables like the Belden ‘Brilliance’ 1505A (RG-59 type) and 1694A (RG-6 type). [there will be other but don’t expect Maplin…….]



    The material of construction

    AV / Audiophile nutters always like to buy the best so can these cables be improved by the use of special materials, well they might!.

    However professional cables (as used by broadcasters) of the highest quality are routinely made without resort to any special materials. These broadcasters depend on the signal getting through with the lowest possible distortion and losses and depend on products from companies like Belden and Canare, made with ordinary high-quality materials.

    Silver cables
    Silver has about 5% lower resistance than the equivalent copper so in practice seems a better material to use. So in theory it should (and is better) BUT

    The resistive loss difference we are talking here is TINY. It is even smaller with silver plated cables! Huge lengths of the coax here have tiny R values so is it relevant? Don’t forget broadcasters have been known to use 1000 feet cables, how long is yours? Gauge of cable can make up for any tiny differences in R

    Silver is more brittle and long term stability of the cable is MUCH worse than in copper based cables.

    Silver oxidises readily in our corrosive atmosphere and forms a passivating layer but so does copper especially if you flux / solder it. Crimp connections can be gas tight.

    There is nothing wrong with silver but do you need it?

    Oxygen Free Copper (OFC) and variants
    The latest casting processes have reduced oxygen content in copper wire to infinitesimally small number. It was never really an issue before and even less so now but is a welcome development. What benefits it brings is… well unproven but it seems like a good idea so why knock it.

    There is nothing wrong with OFC but do you need it?

    Teflon Dielectrics and Insulation
    I was asked the other day what the best dielectric was. I dodged the question. The actual answer is vacuum followed by free air (hence the audiophile ‘nutters’ suspending pure un-insulated copper cables from silk wires in free air). This helps no one in practice but I do like Teflon but why?

    Teflon has certain electrical properties which account for its use / popularity in cables. This is the dielectric constant. This dielectric in a coax cable needs to keep the centre conductor perfectly in the centre of the braid / foil tube (otherwise the CI changes down the cable length as seen in ‘cheap’ coaxs). Polyethylene and Teflon dominate the material used here.

    There is NO DOUBTING Teflon has a lower dielectric constant but there are other more important things happening here.

    If we had nominally identical coax, one with Teflon and one with polyethylene the Teflon one will have a lower C value (great news?). This is after all what we want isn’t it? Well not here!

    The dielectric constant, capacitance, and the CI of the cable are all inter related. Change one and you change the others. So lower C (due to higher dielectric constant) gives us a lower CI (which we don’t want). To get around this we need to reduce the cable diameter and this then makes the C the same as if we used the poorer dielectic, polyethylene, in the first place!! It is all about balance, better dielectrics do not necessarily mean better cables. It is a bit like putting thermal insulation on hot pipes, as you increase the quantity of thermal insulation, the surface area increases rapidly and they eventually end up being radiators and not thermal insulators!

    So why use Teflon at all, well it produces less toxic fumes when it burns! The Plenum rating is why we would use Belden 1695A over the nominal 1694A I am recommending here :) There is no other difference! Now as it is more expensive it should be better shouldn’t it? NO! Electrically they are the same! Unless you have pink coloured heavy electrons….. :)

    Good engineering and tight tolerances are the keys to great cable performance.
     
  7. Nic Rhodes

    Nic Rhodes
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    Hum rejection in unbalanced audio cables (READ Sub woofer cable especially)
    This is where cheap solutions are often recommended despite the fact they may less than optimum. Something to think about!!

    Subs carry signals between 5Hz and say 100 Hz (ish). Unfortunately mains is 50 Hz and it is VITAL that these signals are kept away from the sub cable. This therefore NEEDS to be a mega screened coax for performance. This is the over riding performance issues for sub cables. It is NEVER mentioned here on this forum. All cables should minimise EMF but it is especially important for premium sub performance. At the moment, the wrong cables are being recommended / used for this channel. This is a cheap and cost effective upgrade to go with you ‘Gramma’ / BFD for that dream sub performance. If some one tells you it doesn’t make a difference…….. ;) well you all know cables do make a difference ;)

    Shielding, Shielding and More Shielding. You never have enough for sub operations

    99% of all AV installations carry the signal carried on one wire, accompanied in the cable by another wire or shield which connects the signal grounds of the two pieces of equipment together. If your equipment uses RCA connections, your audio circuits are the normal unbalanced type.

    There is only one way to keep noise out of the signal path, shielding. I have already explained how it works and this is why I (and many others) prefer coax cables for this application (and many others). I have also explained why common mode noise rejection only works for balanced circuits. We are therefore left with shielding as our best defence.

    So what are the shield used?

    Foil shield wound around the dielectric
    braided shield woven from tiny wires
    braid and foil
    multiple braid and / or foil layers.

    Each of the shield types are effective at dealing with different sources of noise.

    Noise can come from say a power cord is EMI Electro Magnetic Interference.
    Noise much higher in frequency is RFI Radio Frequency Interference.

    The signal in the cable dictates whether we more interested in EMI, RFI, or both.

    For video signals, both EMI and RFI are issues. EMI can cause hum bars while RFI will be mistaken for part of the video signal itself and may appear as sparklies in the image.

    For analogue audio, which operates at much lower frequencies, EMI is the principal problem. RFI can enter your system through audio cables, but unless it is particularly strong, ordinarily does not present a noise control issue. We seem obsessed with RFI (RA Kimber) and often forget EMF.

    The two basic shield types, braid and foil, operate differently with respect to EMI and due to coverage and conductivity.

    Braid shields have gaps, and are limited to about 95% coverage. These holes are not particularly significant at low frequencies but at higher frequencies they are (size of wavelengths). Foil shields, very high coverage approaching 100% coverage but they are not nearly so conductive to get that noise away to earth.

    These competing demands of coverage and conductivity mean that the best leads generally use both (and often more than one braid and foil as well). The combination works well for all frequencies.

    EMI often is high energy noise, therefore the conductivity path to ground is important. At sub woofer frequencies it is especially important. Therefore look to double braid coax cables for the sub woofer cable. For RFI (video cables) then a dual foil might be more appropriate a la Belden 1694A and Belden 1505A.

    EMI cause more issues in cables than RFI but both are important.

    [For Sub woofer audio cable I recommend Canare LV-77S]

    Flexibilty and hoods

    For many leads we want a much more flexible lead than the stiffer video leads give us. This is often accomplished by using dual braids on the coax, as discussed above in EMI / sub issues.

    [For flexible cable I recommend Canare LV-77S (stiffest), Belden 1505F and Canare LV-61S (very flexible)]

    For info this also reads of decreasing capacitance ;)

    Colour coded hoods are a god send for video applications (and others), especially when you have 5 connectors to deal with. They cost peanuts to do. Why not ask for them?
     
  8. Nic Rhodes

    Nic Rhodes
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    So what do I recommend (if you got this far!).

    [My biggest issue was working out which cables were better, rather than goinginto specs on each one, this is what I prefer]

    Flexible cables Belden 1505f, Canare LV-61S
    ‘General purpose’ cables Belden 1505f, Belden 1505A, Belden 1694A, Canare LV-77S, Canare LV-61S
    Sub woofer audio Canare LV-77S
    Digital audio Belden 1505A, Belden 1694A (7710 is a colour coded 3 bundle snake of 1694A)
    Analogue video Belden 1505A, Belden 1694A (7710 is a colour coded 3 bundle snake of 1694A)
    Digital video Belden 1505A, Belden 1694A
    Balanced (110 Ohm) Belden 1800A
    SVHS Belden 1808A
    RGBHV Belden 1505A, Belden 1694A (Belden 7712 is a colour coded 5 bundle snake of 1694A AWESOME to look at!)
    Mini RGBHV Belden 1522A

    If you want to substitute Canare, L-5CFB for Belden 1694A, 1505A, no arguments from me.

    [I also quite like the VanDamm small video coax and balanced digital cables as a very decent performing product, widely available but not in the class of the above.]

    Plugs.
    RCA I use crimped Canare, basic models depend on cable type, approaches that 75 ohm CI
    BNCs are Canare again, though there are MANY good crimp BNCs
    XLR analogue Neutrik are my favourites, they come in black :)
    XLR digital Neutrik 110 Ohm CI are my favourites (yes you can get them, most people use the much poorer analogue one ;)

    Connection method
    Crimp / weld where you can, it makes a better connection, soldering is better than bare wire / grub screw but isn’t as good as a crimp.

    Can’t buy off these cables off the shelf easily? Well this is what this forum is for, persuading dealers to stock these cables :D

    You know how to do it The Beekeeper way :D and yes there are many other ways of ‘solving’ this problem. I am a fan of Kimber products as they address ‘certain’ issues very well but they are not screened. All I am doing here is giving you one ‘working’ solution, there are of course MANY others out there.

    Each cable is a careful balance of R, C, L, CI, sheilding and plugs according to it’s use. These may be very different for each application or surprizingly similar.

    Hope this helps someone, felt it needed bringing together. :D
    Some of the material contained in this article was written by Blue Jeans Cable (www.bluejeanscable.com), where additional information on audio and video cables can be found.
     
  9. Stuart Wright

    Stuart Wright
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    Since this article by Beekeeper is so useful, it will remain here indefinitely. I have made a copy of the original thread with the replies in but decided to stick this version with the replies removed.
     
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